Abstract
Empirical models for the characteristic impedance and propagation constant of porous materials given by Delany and Bazley and by the author are generalized with respect to the porosity, the tortuosity and the pore shape factor ratio. The new models have these three parameters besides the flow resistivity. For a practical use, the impedance model can be described with two parameters, the effective flow resistivity and the ratio of tortuosity to porosity. An excellent agreement with Attenborough's four-parameter model shows that the new models are useful for the prediction of acoustical behavior of a wide variety of ground surfaces.
